Shimmed magnetic resonance imaging apparatus and shimming method therefor

Abstract

In a shimming method for an irregular object to be examined by magnetic resonant equipment magnetic field parameters are measured at measurement points located on the surface of an irregular object to be examined. Based on the measured magnetic field parameters, the positions and number of shims for adjusting magnetic field homogeneity are calculated when a passive shimming is to be performed, or the current value in a shimming coil are calculated when an active shimming is to be performed, or at the same time both the positions and number of shims and current value in the shimming coil are calculated when active shimming and passive shimming are to be performed at the same time. Shimming is then performed according to the calculated results. These above steps are repeated until achieving required magnetic field homogeneity. Since the homogeneous region is designed to have an irregular shape, it can provide a better coverage of the irregular object to be examined, and at the same time it reduces the shimming constraints to the unnecessary regions outside the irregular object to be examined, therefore avoiding shimming in those unnecessary regions.